Detection of transits of the nearby hot Neptune GJ 436 b
Abstract
This Letter reports on the photometric detection of transits of the Neptune-mass planet orbiting the nearby M-dwarf star GJ 436. It is by far the closest, smallest, and least massive transiting planet detected so far. Its mass is slightly larger than Neptune's at M = 22.6 ± 1.9 M_⊕ . The shape and depth of the transit lightcurves show that it is crossing the host star disc near its limb (impact parameter 0.84 ± 0.03) and that the planet size is comparable to that of Uranus and Neptune, R = 25 200 ± 2200 km = 3.95 ± 0.35 R_⊕. Its main constituant is therefore very likely to be water ice. If the current planet structure models are correct, an outer layer of H/He constituting up to ten percent in mass is probably needed on top of the ice to account for the observed radius.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 2007
- DOI:
- 10.1051/0004-6361:20077799
- arXiv:
- arXiv:0705.2219
- Bibcode:
- 2007A&A...472L..13G
- Keywords:
-
- stars: planetary systems;
- stars: individual: GJ 436;
- techniques: photometric;
- Astrophysics
- E-Print:
- 4 pages, 3 figures. Accepted for publication in A&